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v2.4.1.9

Changes in Each Component of Accumulated Other Comprehensive Income (Loss) (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified | 3 Months Ended | 9 Months Ended
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Jan. 31, 2015 | Jan. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |
Tax effects on reclassifications of realized net losses | $ 0.3 us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansTax | $ 0.9 us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansTax

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- Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Amount of tax (expense) benefit of reclassification adjustment from accumulated other comprehensive (income) loss related to pension and other postretirement defined benefit plans. + References No definition available. + Details
Name: | us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansTax
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration